The invention relates to an improved method for the recovery of terephthalates of alkali metals or alkaline-earth metals or of terephthalic acid and of alkylene glycol by saponification of a polyalkylene terephthalate. It relates more particularly to the continuous production of terephthalates of alkali metals or alkaline-earth metals from polyalkylene terephthalates.
It allows improved recycling of polyalkylene terephthalate waste originating, for example, from films, fibers or used bottles. The method according to the invention further allows recovery of alkylene glycol of good purity, for re-use.
Alkaline saponification of polyalkylene terephthalate in solution is described in the prior art (see, for example, U.S. Pat. No. 3,317,519 and U.S. Pat. No. 3,544,622); it is generally performed in solution diluted in water or in glycol, generally under pressure.
In patent application French Patent No. 2,672,049,the applicants have described a method for manufacturing terephthalates of alkali metals or alkaline-earth metals by heating polyalkylene terephthalate with an alkali metal hydroxide or an alkaline-earth metal hydroxide, in the absence or the presence of water.